Thermostat



June 28, 193,2.y J. A. SPENCER THERMOS TAT Filed Sept. 6, 1930 2 Sheets-Shee l June 28, 1932.

J. A. SPENCER THERMOSTAT Filed sept. e. 195o 2` sheets-sheet 2 Patented June -28, 1932 UNITED STATES PATENT ori-ICE JOHN A. SPENCER, OF NEWTONV ILLE, MASSACHUSETTS, ASSIGNOR T GENERAL PLATE COMPANY, 0E ATTLEBORO, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS THERMOSTAT Application led September 6, 1980. Serial No. 486,152.

of a device of the class described adapted to be manually reset; and the provision of a dev vice of this character which is simple and compact in form and positive in operation.

Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structure hereinafter described,Y and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which are illustrated several of various possible embodiments of the invention,

Fig. 1 is a cross section of a switch embodyin the invention, taken on line 1-1 of Fig. 2;

ig. 2 is a horizontal section taken on line Fig. 3 isa longitudinal section showing an alternative form of the invention; and,

Fig. 4 is a longitudinal section showing another modification.

Similar reference characters indicatecorresponding parts throughout the several views of the drawings.

Referring now more particularly to Fig. 1,

there is illustrated kat numeral 1 a swltchplate carrying a porcelain or like cover 3, said cover 3 having'a circular groove 5 therein for holding a heating element 7. The heating element 7 is in series connection with an outside circuit 9 and a series of line terminals 11, said terminals 11 being mounted on the plate 1 in suitable insulated relationship.

n Terminal'` engaging elements 15 are mount- 0 ed on a cup-,Shaped steel or like disc 17 for purposes of moving into and out of engagement with the contiguous terminals 11 for making and breaking the circuit at a series of points, substantially simultaneously. Three points of break are shown for example. Movement is effected by snap action of the disc which has been manufactured in the shape shown by the dotted-lines but which whenexternally forced to assume the solidline lposition, will retain that position, provide all parts thereof are at substantially equal temperatures. This is because the rim is then under tangential tension and the inner portionvunder radial compression, these set- (tiing up a resistance to return action'of the isc. I

The mechanism for permitting snap action ofthe disc 17 from the dotted to the solidline position comprises a manually operable pin 19 having a grooved head 21 for controlllng movement of the disc 17 at a central opening 22. This pin 19 is reciprocable in an adjustable bushing 23. Studs 25 havin heads 27 pass losely through the disc l and provide, by means of said heads 27, reaction pieces or abutments against which the disc 17 may in its dottedline position be pushed so as to force it to assume the solid-line position with a snap action.

Under steady temperature conditions, the disc will tend to remain in the solid-line position. It may be adjusted to react or bulge upwardly against the heads 27, thereby providing a positive reaction between the contacts 15 and the line terminals 11, or this feature may be eliminated.

Operation is as follows:

When the disc is in the solid-line position, the circuit is closed and the heater 7 being in series, warms. As long as the current is of normal value, temperature' rise upon circuit closing will be relatively-slow in the heater and conditions of substantial thermal equilibrium in the disc will be Vreached without differentially expanding the periphery of the disc to a degree to cause the stressed center to snap through its then tensioned periphery. However, if a sudden temperature rise occurs in the heater 7, as upon short 190 "rfiv circuit, the periphery of the disc will be suddenly heated at a relatively high rate of temprature rise, the rate of rise in the center ing less, because of the unstable thermal conditions, heat not having had time to travel to the center. This causes the rim portion of the disc to expand relatively rapidly, thus permitting the internal stresses in the central portion to drive said central portion with a snap action thro h the periphery and into the normal dotte -line position. Resetting may then be manually accomplished after thermal equilibrium has again been reached.

From the above it will be seen that the device is responsive only to temperature changes of predetermined rapidity, the exact degree dependin upon the initial tension placed in the disc y the adjusting means and upon design constants.

Advantages of the device are that it is simple. It is not, iniuenced by ambient geimperature which heats or cools the whole It is useful for example in an electric plug, to replace a, fuse plug as an overload release. Sudden increase of current operates the device but a slow increase of current will not operate the device because, as above shown the heat escapes and/or equilibrates. In the plug a reset device might comprise a button, accessible to a nail or the like, through -a hole, and accessible only when the plug is out of the socket.

In Fi 4 is shown a modification wherein the heatlng coil 7 is not used. In this example the switch 29 has a snap-acting disc for circuit closing and opening purposes, this bein as above described. The circuit made and roken is caused to operate aheater for the medium in which the thermostat is immersed. The switch pin 19 is under two-way control by a spring= 31 and lever 33, the latter being fulcrumed at 35 and engaging at 37 a rod 39 having a given thermal coeiiicient of expansion.

About the rod 39 is a tube 41 held to the plate 43 which supports the switch 29. The tube has a coeiicient of expansion substantially equal to that of the rod. They are joined at 45.

It will be seen that for slow 'rises in temterature of the ambient medium, the tube 41 and rod 39 have the same temperature rise. Hence one does not change its length with respect to the other and no movement occurs in the lever 33.

But if the temperature rise be fast (above a given or predetermined rate), the outer tube 41 will be heated faster than the inner rod 39, thus causing relative movement or Vchange in length and finally movement of the switch to snap open, thus for example closing off a heater whlch is supplying heat to the medium. The temperature ris'e is thus checked or reduced until stable enough conditions are reached that both rod 39 and tube 41 have the same or vnearly the same tempera ture, so that the switch is re-closed. Another thermostat ma be used to limit the ultimate temperature o the medium, or the rod 39 and tube 41 herein may be given some diiference in coeiiicients of expansion, whereby after enough temperature rise (even steady), enough accrued diierencein len hs will be attained to throw the switch. us in one device may be had the advantages of ultimate temperature limitations with limitations on rate of temperature change. It will be understood that the switch may also operate inversely, that is, to open under the given conditions. It is also evident that the disc in the example of Fig. 4 may be maintained at a steady temperature, or if it is subjected to suddenly fluctuating temperatures, it Vmay be ymade s0 as not to spring automatically from one of the positions to another when unequally heated, but to tend to maintain either extreme position when set therein by external means.

In Fi 3 is shown another application wherein ot and cold water (proportioned as desired elsewhere) is brought in at numerals 51 and 53 respectively into a casing 55, suitabl baiiied at 57. The mixture leaves at an out et 58. y

A valve 59 is directed to open against the hot flow at 51, said valve 59 having a stem 61 ending in a shield 63. The shield 63 engages a second shield 65, thelatter having a reset handle 67 associated therewith externally of the casing 55.

The shields 63, have closely juxtaposed but spaced peripheries 69, loosely accommodating a disc 71, analogous to the one described in connection with Fig. 1. The disc 71 is peripherally fulcrumed between rows of projections 73 which permit passage of water around, the disc.

Operation is as follows:

The handle 67 is pushed up, thus opening the valve and straining the disc 71 to the dotted-line position. This dotted-line position of the disc 71 will be maintained under conditions of thermal equilibrium at or near the temperature of the hot-cold mix of ambient medium, the handle 67 being held in long?- enough for thermal equilibrium to be established'in the disc, if it has not already been established. It is to be understood that the valves controlling the hot and Coldwater iow have been adjusted for proper temperature of mix.

Under these conditions, should there be a sudden increase inl the proportion of hot water, caused, for example, by someone else on the lines making a heavy draft of cold water, the temperature of the mix mi ht become `dangerously high, for instance or someone under a bath shower.

p But the present device cuts off the iiow under these conditions, for the suddenly heated Water which is deflected by the shields 63, to pass around Vthe disc edges, relieves the peripheral tension in the disc. The center of the disc is cooler because its tem rature has not had time to rise. Thus the isc snaps to the position shown to close the ivalve.

Slow temperature increase, such as is had by adjusting the relative hot and cold water flows is permitted, because the whole disc heats more slowly and thus the relation between peripheral tension and radial compression is maintained without a consequent snapping action to open the valve. Slow' temperature rises due to other causes are not dangerous because they can be incipiently felt or otherwise detected, before they become extreme. v

In view of the above, it will be seen tha the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made incarrying out the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpretedv as illustrative and not in a limitingsense.

I claim:

1. A thermostat comprising a cupped disc having a normal cupped position but adapted to be sprung to a stressed, cupped position from whence it can spring to the normal position upon relieving peri heral stresses therein, means operated-by said disc and means for changing the temperature of the periphery of the disc at a diiferent rate than the remainder, whereby it can spring from the stressed position to the normal position.

2. A thermostat comprising a cupped disc having a normal cupped position but adapted to be sprung to a stressed, cupped position from whence it can spring to the normal position upon relieving peripheral stresses therein, means operatedv by said disc and means for changing the temperature of the periphery of the disc at a different rate than the remainder, whereby it can spring from the stressed position to the normal position, said last-named means comprising heating means adapted to heat the disc at the periphery thereof.

3. A thermostat comprising a snap-acting normally cupped disc said disc being adapted to take a positionot reverse curvature and maintain said last-named osition as long as unrelieved stresses exist t erein and means for applying heat unequally to diil'er'ent portions of the disc for relieving said stresses, whereby the disc assumes its normal position.

4. vA thermostat comprising a snap-acting normally curved sheet, said sheet being adapted to take a position of reverse curvature and maintain said last-named position as long as unrelieved stresses exist therein and means for applying heat unequally to diiierent portions of the sheet for relieving said stresses, whereby the sheet assumes its normal position.

5. A thermostat comprising a sheet having a normal predetermined position but adapted to b e forcibly sprung and to maintain itself stressed in another position, from whence it can spring to its said normal predetermined position upon the relief of peripheral stresses engendered therein, means associated with the thermostat adapted tov effect a change of temperature of said periphery at a rate which is greater than the rate at which the temperature of the remainder of the disc increases, whereby said peripheral stresses are relieved.

6. A thermostat comprising a snap-acting, normally positioned single-layer sheet, said sheet being-adapted to take another position and maintain said last-named position as long as resulting unrelieved stresses 'exist therein, and means for distributingheat unequally to different portions of the sheet for at least partially relieving said stresses, whereby the sheet is caused to assume its normal position.

In testimony whereof, I haveisigned my name to this specification this 8th day of August, 1930.

x JOHNA. SPENCER. 

